VISUAL INSPECTION
Visually inspect all electrical wiring, looking for chafed, stretched, cut or pinched wiring. Ensure electrical connectors fit tightly and are not corroded. Ensure vacuum hoses are properly routed and are not pinched or cut. See VACUUM DIAGRAMS article in this section to verify routing and connections (if necessary). Inspect air induction system for possible vacuum leaks.
MECHANICAL INSPECTION
| WARNING | DO NOT use ignition switch during compression tests on fuel injected vehicles. Use a remote starter to crank engine. Fuel injectors on many models are triggered by ignition switch during cranking mode, which can create a fire hazard or contaminate engine's oiling system. |
Diagnostic Aids
Water or foreign material in fuel can cause no-start condition during freezing weather. Engine may start after 5-6 minutes in heated shop. Problem may not reoccur until vehicle is parked overnight in freezing temperature. Low fuel pressure can result in a very lean air/fuel ratio. Fouled or damaged spark plugs will also cause a no-start condition. See TESTS W/O CODES article in this section.
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Scheme 2
Fuel spray may be present at injector, but may not be enough to start engine. If both fuel injector and related circuits are okay, check for a partially blocked injector nozzle.
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Scheme 4
CHART A-7A, FUEL SYSTEM DIAGNOSIS (FUEL PUMP RELAY CHECK)
When ignition is turned on, ECM energizes fuel pump relay for 3 seconds, allowing fuel pump operation. When fuel pump relay is de-energized, fuel pump stops operating. If engine is being cranked or is running, fuel pump will continue to operate as long as ECM is receiving ignition reference pulses. If ignition reference pulses are not detected, fuel pump will stop after 3 seconds.
Note. Test numbers refer to numbers on diagnostic chart.
- Verifies fuel pump operation with ignition on.
- Checks fuel pump relay switch for power.
- Checks for faulty ECM or improper fuel pressure.
- Checks fuel pump circuit.
- Checks for open in Pink/Black wire.
- Checks for power at fuel pump relay coil.
- Checks for a faulty fuel pump or an open in Black wire.
- Checks for faulty fuel pump relay.
- Checks for faulty ECM and an open in Pink wire.
Visually inspect wiring and connectors if intermittent problem exists.
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Scheme 6
CHART A-7B, FUEL SYSTEM PRESSURE TEST
When ignition is turned on, ECM energizes fuel pump relay for 3 seconds, allowing fuel pump operation. When fuel pump relay is de-energized, fuel pump stops operating. If engine is being cranked or is running, fuel pump will continue to operate as long as ECM is receiving ignition reference pulses. If ignition reference pulses are not detected, fuel pump will stop after 3 seconds.
Fuel pump delivers fuel through fuel filter to fuel injector and fuel pressure regulator, where system pressure is controlled at 34-41 psi (2.4-2.9 kg/cm 2 ). Excess fuel returns to fuel tank through fuel return line.
Note. Test numbers refer to numbers on diagnostic chart.
- Verifies if fuel pressure is within specification.
- Checks fuel feed pipe and hose for leaks.
- Checks for faulty fuel pump and faulty pressure regulator.
- Checks for leaky fuel injector, throttle body or for a faulty fuel pressure regulator.
- Checks for leaks at fuel pump hose connections, faulty fuel pump or a faulty fuel pressure regulator.
- Checks for restricted fuel feed pipe, faulty fuel filter or restricted fuel return line.
Improper fuel pressure may cause following conditions: hard starts, engine cranks but will not start, engine cuts out, hesitation, loss of power and poor fuel economy.
